Forming Interconnect Structures Using Pre-Ink-Printed Sheets

ABSTRACT

A method of forming a device includes printing conductive patterns on a dielectric sheet to form a pre-ink-printed sheet, and bonding the pre-ink-printed sheet onto a side of a substrate. The conductive feature includes a through-substrate via extending from a first major side of the substrate to a second major side of the substrate opposite the first major side. A conductive paste is then applied to electrically couple conductive patterns to a conductive feature in the substrate.

TECHNICAL FIELD

This disclosure relates generally to integrated circuit structures, and more particularly to forming interconnect structures for integrated circuits using pre-ink-printed sheets.

BACKGROUND

Among the efforts for reducing the size of integrated circuits and reducing RC delay, three-dimensional integrated circuits (3DICs) and stacked dies are commonly used. Through-silicon vias (TSVs) are thus used in 3DICs and stacked dies. In this case, TSVs are often used to connect the integrated circuits on a die to the backside of the die. In addition, TSVs are also used to provide short grounding paths for grounding the integrated circuits through the backside of the die, which may be covered by a grounded metallic film.

TSV connections often require redistribution lines to be formed on the backside of wafers and connected to TSVs. Conventional backside TSV interconnections were formed using processes, such as chemical vapor deposition (CVD) methods, physical vapor deposition (PVD) methods, lithography processes, etching processes, and/or the like. These methods involve high costs. Further, these methods often require elevated temperatures of wafers, typically 200 to 400 degrees centigrade. Accordingly, thermally-induced stresses were introduced into the resulting wafers and chips and caused warpage of the wafers/chips. Furthermore, breaking of the dielectric layers and delamination between the dielectric layers in the wafers/chips may also occur.

SUMMARY

In accordance with one aspect, a method of forming a device includes printing conductive patterns on a dielectric sheet to form a pre-ink-printed sheet, and bonding the pre-ink-printed sheet onto a side of a substrate. The conductive feature includes a through-substrate via extending from a first major side of the substrate to a second major side of the substrate opposite the first major side. A conductive paste is then applied to electrically couple conductive patterns to a conductive feature in the substrate.

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGS. 1 through 9 are cross-sectional views and a top view of intermediate stages in the manufacturing of an interconnect structure comprising pre-ink-printed redistribution lines in accordance with various embodiments; and

FIG. 10 illustrates the cross-sectional view of an interposer in accordance with alternative embodiments, wherein the interconnect structures on opposite sides of the interposer comprise pre-ink-printed redistribution lines.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative and do not limit the scope of the disclosure.

A novel interconnect structure, which may be connected to through-substrate vias (TSVs), and the method of forming the same are provided in accordance with an embodiment. The intermediate stages in the manufacturing of the embodiment are illustrated. The variations of the embodiment are discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

Referring to FIG. 1, wafer 2, which includes substrate 10 and integrated circuits 4 therein, is provided. In accordance with various embodiments, wafer 2 is a device wafer comprising active integrated circuit devices, such as transistors. Substrate 10 may be a semiconductor substrate, such as a bulk silicon substrate, although it may include other semiconductor materials, such as silicon germanium, silicon carbide, gallium arsenide. Semiconductor devices such as transistors (also symbolized by block 14) may be formed at the front surface 10 a of substrate 10. Interconnect structure 12, which includes metal lines 9 and vias 11 formed therein, is formed over substrate 10, with the metal lines and vias being electrically coupled to the semiconductor devices. Metal lines 9 and vias 11 may be formed of copper or copper alloys, and may be formed using the well-known damascene processes. Interconnect structure 12 may include commonly known inter-layer dielectrics (ILDs) and inter-metal dielectrics (IMDs). Metal bumps 15, which may be solder bumps or copper bumps, are formed on the front side (the side facing up in FIG. 1) of wafer 2, and protrudes beyond the front surface of wafer 2.

In alternative embodiments, wafer 2 is an interposer wafer, and is substantially free from integrated circuit devices including active devices, such as transistors and diodes, formed therein. Substrate 10 may be formed of a semiconductor material or a dielectric material, such as silicon oxide. Furthermore, interposer wafer 2 may include, or may be free from, passive devices, such as capacitors, resistors, inductors, varactors, or the like.

TSVs 20 are formed in substrate 10. In an embodiment, as shown in FIG. 1, TSVs 20 may be formed using a via-first approach, and may be formed before the formation of interconnect structure 12. Accordingly, TSVs 20 extend into the IMD layers in interconnect structure 12, and may, or may not, extend into ILD 17 that is used to cover the semiconductor devices. In alternative embodiments (not shown), TSVs 20 are formed using a via-last approach, and are formed after the formation of interconnect structure 12. Accordingly, TSVs 20 penetrate through interconnect structure 12. Isolation layers 22 are formed on the sidewalls of TSVs 20, and electrically insulate TSVs 20 from substrate 10. Isolation layers 22 may be formed of commonly used dielectric materials, such as silicon nitride, silicon oxide (for example, tetra-ethyl-ortho-silicate (TEOS) oxide), and the like.

Referring to FIG. 2, wafer 2 is bonded onto carrier 16 through glue 18, and a backside grinding is performed to remove an excess portion of substrate 10. For example, a chemical mechanical polish (CMP) is performed to the backside of substrate 10, so that TSVs 20 are exposed. Backside insulation layer 24 is formed to cover the backside of substrate 10. In an exemplary embodiment, the formation of backside insulation layer 24 includes etching back back surface 10 b of substrate 10, blanket forming backside insulation layer 24, and performing a light CMP to remove the portion of backside insulation layer 24 directly over TSVs 20. Accordingly, TSVs 20 are exposed through backside insulation layer 24. In alternative embodiments, the openings in backside insulation layer 24, through which TSVs 20 are exposed, are formed by etching. In the resulting structure, TSVs 20 include TSV bumps 20A, which are portions of TSVs 20 protruding out of the back surface of wafer 2.

FIGS. 3A and 3B are a top view and a cross-sectional view of pre-ink-printed sheet 30, wherein the cross-sectional view shown in FIG. 3B is obtained from the plane crossing line 3B-3B in FIG. 3A. In an embodiment for forming pre-ink-printed sheet 30, dielectric sheet 32 is provided. Dielectric sheet 32 may have a size matching the size of wafer 2. The thickness T1 (FIG. 3B) of dielectric sheet 32 may be between about 1 μm and about 100 μm, for example. It is realized, however, that the dimensions recited throughout the description are merely examples, and may be changed. In an embodiment, dielectric layer 32 is formed of polyimide, although other dielectric materials, such as BCB, Phenol, Epoxy, or the like may also be used. Through-holes 34, which extend from one side of dielectric layer 32 to the opposite side, are formed at desirable positions of dielectric layer 32. Although the illustrated through-holes 34 are circular, they may also have other shapes, such as square, hexagon, or the like. The size of through-holes 34 is slightly greater than TSV bumps 20A as in FIG. 2.

Conductive lines (also referred to as redistribution lines (RDLs) hereinafter) 36 are printed on dielectric layer 32 using ink-printing, wherein the ink may be a conductive paste, such as a silver paste, a copper paste, or the like. The ink-printing may be performed using, for example, a nano silver ink printer. Some of RDLs 36 extend to the edges of through-holes 34. In an embodiment, the width W of RDLs 36 may be greater than about 10 μm, or even greater than about 14 μm, while thickness T2 of RDLs 36 may be less than about 2 μm, although different thicknesses and widths may be used, depending on the capability of the ink-printer. If thicker RDLs 36 are desirable, repeated printing may be performed, with each of the printings resulting in the increase in the thickness T2 of RDLs 36.

Besides RDLs 36, vias 38 may also be formed. Throughout the description, RDLs and vias are also referred to as conductive patterns. In an embodiment, vias 38 are also formed by ink-printing. Referring to FIG. 3B, the formation of vias 38 includes repeated printing of the conductive paste onto RDLs 36, until thickness T3 of vias 38 reaches desirable values, for example, greater than about 1 μm. In alternative embodiments, no vias 38 are formed. The printing of RDLs 36 and vias 38 may be performed in a same printing step.

Referring to FIG. 4, after the formation of pre-ink-printed sheet 30, pre-ink-printed sheet 30 is laminated onto the backside of wafer 2. Dielectric layer 32 may be laminated (bonded) to the backside of wafer 2 through a thin glue layer (not shown) or by heating wafer 2 so that dielectric layer 32 (for example, a polyimide layer) adheres to wafer 2. An alignment is performed so that TSV bumps 20A extend into through-holes 34. Next, as shown in FIG. 5, conductive paste 39, which may also be a silver paste, a copper paste, or the like, is filled into through-holes 34, and to electrically couple TSVs 20 to RDLs 36.

FIGS. 6 through 8 illustrate the formation and the bonding of pre-ink-printed sheet 40. Referring to FIG. 6, pre-ink-printed sheet 40 is pre-formed, for example, using essentially the same methods as forming pre-ink-printed sheet 30. Pre-ink-printed sheet 40 comprises dielectric sheet 42, on which RDLs 46 and vias 48 are formed using ink-printing. The patterns of through-holes 44, RDLs 46, and vias 48 in pre-ink-printed sheet 40 may be different from that of respective through-holes 34, RDLs 36, and vias 38. Further, the locations of through-holes 44 correspond to the locations of vias 38, and the size of through-holes 44 are slightly greater than that of vias 38 so that vias 38 may fit in through-holes 44.

Referring to FIG. 7, pre-ink-printed sheet 40 is placed on, aligned to, and laminated (bonded) onto pre-ink-printed sheet 30. Vias 38 extend into through-holes 44. Next, as shown in FIG. 8, conductive paste 49 is filled into the remaining spaces of through-holes 44, and electrically couples vias 38 to RDLs 44. In the embodiments wherein no vias 38 are formed on pre-ink-printed sheet 30, conductive paste 39 fills the entireties of through-holes 44, and electrically couples RDLs 36 to RDLs 46.

FIG. 7 illustrates that gaps 52 may exist between pre-ink-printed sheets 30 and 40. As shown in FIG. 8, gaps 52 may be filled with filling dielectric material 54, which may be an epoxy. In alternative embodiments, filling dielectric material 54 may be applied onto pre-ink-printed sheet 30 after the structure as shown in FIG. 5 is formed, but before pre-ink-printed sheet 40 is laminated onto pre-ink-printed sheet 30.

After the bonding of pre-ink-printed sheet 40, additional pre-ink-printed sheets may be bonded to form multi-layer RDLs. As shown in FIG. 9, pre-ink-printed sheet 50, which includes additional RDLs 56, is pre-formed and then bonded onto pre-ink-printed sheet 40. Bumps 60 may then be formed. Bumps 60 may be solder bumps, copper bumps (which may be coated with nickel layers, gold layers, or the like) may then be formed.

FIGS. 1 through 8 illustrate the formation of backside interconnect structure for a device wafer comprising TSVs. In alternative embodiments, the teaching of the present disclosure is readily applicable to the formation of interconnect structures on one side, or both sides, of interposer wafers, which do not have active devices, such as transistors therein. A cross-sectional view of an exemplary embodiment is shown in FIG. 10. It is observed that the interconnect structures on both sides of interposer wafer 2 may be formed using pre-ink-printed sheets.

In the embodiments, the interconnect structures and the respective RDLs are formed using pre-ink-printed sheets. Therefore, the high-cost processes, such as chemical vapor deposition (CVD) methods, physical vapor deposition (PVD) methods, lithography processes, etching processes, and the like, are avoided. Further, the formation processes of the embodiments are substantially free from high-temperature processes, and hence substantially no thermally-induced stresses are introduced into the resulting wafers and dies as a result of the formation of interconnect structures.

Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the disclosure. 

1. A method of forming a device comprising: providing a substrate comprising a conductive feature, wherein the conductive feature comprises a through-substrate via extending from a first major side of the substrate to a second major side of the substrate opposite the first major side; providing a first dielectric sheet; printing first conductive patterns on the first dielectric sheet to form a first pre-ink-printed sheet; bonding the first pre-ink-printed sheet onto a first side of the substrate; and applying a conductive material to electrically couple the first conductive patterns to the conductive feature of the substrate.
 2. The method of claim 1 further comprising: providing a second dielectric sheet; printing second conductive patterns on the second dielectric sheet to form a second pre-ink-printed sheet; bonding the second pre-ink-printed sheet onto the first pre-ink-printed sheet; and applying an additional conductive material to electrically couple the second conductive patterns to the first conductive patterns.
 3. The method of claim 1 further comprising: providing a second dielectric sheet; printing second conductive patterns on the second dielectric sheet to form a second pre-ink-printed sheet; bonding the second pre-ink-printed sheet onto a second side of the substrate opposite the first side; and applying an additional conductive material to electrically couple the second conductive patterns to the conductive feature in the substrate.
 4. The method of claim 1, wherein the method of printing comprises an ink-printing using a conductive paste as an ink.
 5. The method of claim 1 further comprising forming a through-hole in the first dielectric sheet.
 6. The method of claim 5, wherein after the step of bonding the first pre-ink-printed sheet onto the first side of the substrate, the conductive feature extends into the through-hole.
 7. The method of claim 1, wherein the step of printing first conductive patterns comprises: printing on a portion of the dielectric sheet to form redistribution lines; and printing on portions of the redistribution lines to form vias directly over, and contacting, the portions of the redistribution lines.
 8. A method of forming a device comprising: providing a substrate comprising a through-substrate via (TSV) extending from a first side of the substrate to a second side of the substrate opposite the first side; forming a first pre-ink-printed sheet comprising: a first dielectric sheet; and first conductive patterns over and contacting the first dielectric sheet; bonding the first pre-ink-printed sheet onto the first side of the substrate, wherein a top portion of the TSV extends into a first through-hole in the first dielectric sheet; and applying a conductive paste to fill a remaining space of the first through-hole and electrically coupling one of the first conductive patterns to the TSV.
 9. The method of claim 8 further comprising: forming a second pre-ink-printed sheet comprising a second dielectric sheet, and second conductive patterns over and contacting the second dielectric sheet; bonding the second pre-ink-printed sheet onto the first pre-ink-printed sheet; and electrically coupling the second conductive patterns to the first conductive patterns.
 10. The method of claim 9, wherein the second pre-ink-printed sheet comprises a second through-hole, and wherein the first conductive patterns comprise a via extending into the second through-hole.
 11. The method of claim 8, wherein the first conductive patterns comprise redistribution lines and vias over and contacting the redistribution lines, and wherein the first conductive patterns are formed by printing an additional conductive paste onto the first dielectric sheet using the additional conductive paste as an ink.
 12. The method of claim 11, wherein the first through-hole is formed before the step of printing.
 13. The method of claim 11, wherein the first through-hole is formed after the step of printing.
 14. A method of forming a device comprising: forming a first pre-ink-printed sheet comprising: providing a first dielectric sheet; and printing a conductive paste onto the first dielectric sheet to form a first conductive pattern; forming a second pre-ink-printed sheet comprising: providing a second dielectric sheet; and printing the conductive paste onto the second dielectric sheet to form a second conductive pattern; bonding the first pre-ink-printed sheet onto a substrate comprising a TSV in the substrate; electrically coupling the first conductive pattern to the TSV; bonding the second pre-ink-printed sheet onto the first pre-ink-printed sheet; and applying an additional conductive paste to electrically couple the first conductive pattern to the second conductive pattern.
 15. The method of claim 14, wherein the conductive paste comprises a silver paste.
 16. The method of claim 14, wherein the second dielectric sheet comprises a through-hole, and wherein the additional conductive paste is filled into the through-hole to electrically couple the first conductive pattern to the second conductive pattern.
 17. The method of claim 16, wherein the first conductive pattern further comprises a via, and wherein after the step of bonding the second pre-ink-printed sheet onto the first pre-ink-printed sheet, the via extends into the through-hole.
 18. A device comprising: a substrate comprising a through-substrate via (TSV) extending from a first side of the substrate to a second side of the substrate opposite the first side; a dielectric sheet over the substrate; and a redistribution line over the dielectric sheet, wherein the redistribution line is formed of an ink, and is electrically coupled to the TSV through a through-hole in the dielectric sheet.
 19. The device of claim 18, wherein the TSV comprises a portion extending into the through-hole.
 20. The device of claim 19 further comprising a conductive paste filling a remaining portion of the through-hole. 